1. Field of the Invention
The present invention first relates to a method for heating a fluid line system with at least two electric heating elements.
Furthermore, the invention also relates to a heating system for a fluid line system with at least two electric heating elements, and, in particular, for application of the method according to the present invention.
2. Related Technology
For the related technology, reference is made to documents DE 41 35 082 C1, WO 2007/073286 A1, EP 1 985 908 A1 and also EP 1 765 541 A1, for example.
Heatable fluid line systems are, in particular, frequently used in motor vehicles, namely for such media that tend to freeze even at relatively high ambient temperatures due to their freezing point. Thus, certain functions can be affected. This is the case, for example, with water lines for the windshield washer system, but especially also for lines for aqueous urea solution which is used as a NOx-reduction additive for diesel engines with so-called SCR catalyst units. Therefore, the electric heating elements can be activated at low temperatures in order to prevent freezing, or to thaw an already frozen medium.
Fluid line systems of this kind usually consist of at least one fluid line (tubing or hose line)—cf. in particular EP 1 985 908 A1 (FIGS. 13, 14) and also WP 2007/073286 A1—with two line connectors (plug connectors) at the ends. The fluid line has an electric heating element in the form of a helical heating wire wrapping over the length of the line, for example, and/or at least one of the line connectors (WP 2007/073286 A1) and/or each of the two connectors (EP 1 985 908 A1) is likewise provided with an electric heating element, in particular in the form of a heating wire wrapping. Usually all heating elements are electrically connected in series and can be connected to a common current and/or voltage supply (cf. in particular EP 1 985 908 A1, FIGS. 14a, 14b). This raises the problem that, in terms of their heating power, the individual heating elements have to be designed specifically for the particular line system, namely in adaptation to the length of the respective fluid line. This results in a great effort for providing different embodiments.
Document EP 1 764 541 A1 describes a heatable fluid line in which there is at least one electric heating conductor at the perimeter of the conducting tube and at least two electric supply lines running in the longitudinal direction of the conducting tube, wherein the heating conductor is alternatingly connected electrically to one of the two power supply lines, namely alternatingly to the plus pole and minus pole of the supply voltage. In this regard the connecting points seen in the longitudinal direction of the conducting tube are arranged equally spaced and one behind the other. The electric heating conductor is connected to the supply lines e.g. by soldering, welding or crimping. Due to this configuration, the fluid line has a constant heating power per length unit. As a result, the fluid line can be prefabricated in large lengths and cut to the required length, wherein each cut-to-length line length has the same heating power per length unit. This known fluid line has, however, the disadvantage that relatively high material costs will result, since in addition to the electric heating conductor or to the heating conductors, at least two supply lines have to be respectively be provided. An increased manufacturing effort also results from the required alternating connection points between the heating conductor and the supply lines. Each heatable fluid line prefabricated in this way has a defined heating power per length unit. But if different heating powers per length unit are required for different applications, prefabrication of differently heatable fluid lines with the respectively required heating power per length unit is necessary, so that the prefabricated fluid lines have to be stocked up or stored. This results in additionally increased production costs.